1. Field of the Invention
The present invention relates to a method of manufacturing a field-effect transistor, a field-effect transistor, and a method of manufacturing a display device.
2. Description of the Related Art
In recent years, flat panel displays (FPD) have been put into practical use due to the progress of a liquid crystal technique, an electroluminescence (EL) technique, etc. In particular, since organic electroluminescence devices (hereinafter referred to as an “organic EL device”) using thin film materials that are excited by the application of a current to emit light can obtain high-intensity luminescence at a low voltage, a reduction in the thickness, weight, dimension, and electricity consumption of the devices have been expected in a wide range of fields including cellular-phone displays, personal digital assistants (PDA), computer displays, information displays of automobiles, TV monitors, or common lighting. These FPDs are driven by an active matrix circuit of field-effect transistors (hereinafter sometimes referred to as TFT) in which an amorphous silicon thin film or a polycrystalline silicon thin film provided on a glass substrate is used for an active layer.
In contrast, it has been attempted to use a resin substrate that is lightweight and has flexibility in place of a glass substrate in order to achieve a further reduction in the thickness of the FPDs, a reduction in the weight thereof, and an improvement of breakage resistance thereof. However, the manufacturing of the transistors using a silicon thin film requires a relatively high-temperature heating process and is difficult to directly form on a resin substrate generally having low heat resistance. Then, the development of TFTs using an amorphous oxide semiconductor allowing film forming at low temperatures has been actively performed. The amorphous oxide semiconductor can form a film at room temperature and can be formed on a film, and thus has attracted attention as a material for the active layer in TFTs.
The amorphous oxide semiconductor is known to be susceptible to acid. Therefore, by providing an acid-resistant layer on the active layer, the active layer containing the amorphous oxide semiconductor is protected from an acid to be used in the manufacturing process for TFTs (e.g. Japanese Patent Application Laid-Open (JP-A) No. 2008-166716 and APPLIED PHYSICS LETTERS, 90, 212114 (2007)). The documents propose providing a layer containing SiO2 on the active layer as a layer for protecting the active layer.